Coding and decoding method and device on multi-level image

Abstract

A coding and decoding method includes the step of a) classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; b) coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and c) decoding coded data according to a linear interpolation scheme, a cubic-function convolution scheme or an interpolation scheme having smoothing performance for generating pixel values included in the non-edge part.

1. A coding and decoding method, comprising the steps of:
 a) classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and 
 c) decoding coded data according to a linear interpolation scheme for generating pixel values included in the non-edge part. 
 
   
   
     2. The method as claimed in  claim 1 , wherein, when a picture regarding mode is selected, the input image is coded according to a coding scheme prepared for the non-edge parts is applied regardless of result of said step a). 
   
   
     3. A coding and decoding method, comprising the steps of:
 a) classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and 
 c) decoding coded data according to a cubic-function convolution interpolation scheme for generating pixel values included in the non-edge part. 
 
   
   
     4. The method as claimed in  claim 3 , wherein, when a picture regarding mode is selected, the input image is coded according to a coding scheme prepared for the non-edge parts is applied regardless of result of said step a). 
   
   
     5. A coding and decoding method, comprising the steps of:
 a) classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and 
 c) decoding coded data according to an interpolation scheme having smoothing performance for generating pixel values included in the non-edge part. 
 
   
   
     6. The method as claimed in  claim 5 , wherein, when a picture regarding mode is selected, the input image is coded according to a coding scheme prepared for the non-edge parts is applied regardless of result of said step a). 
   
   
     7. A coding method comprising the steps of:
 a) dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; and 
 c) classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part, 
 wherein said step b) controls the coding scheme according to the result of classification in said step c). 
 
   
   
     8. A coding method comprising the steps of:
 a) dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; and 
 c) classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part, 
 wherein said step a) controls a determination threshold thereof according to the result of classification in said step c). 
 
   
   
     9. A coding method comprising the steps of:
 a) dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; and 
 c) classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part, 
 wherein said step a) controls a determination threshold thereof according to the result of classification in said step c) and a set image characteristic mode. 
 
   
   
     10. A coding and decoding method comprising the steps of:
 a) dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 b) coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; 
 c) classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part; and 
 d) decoding coded data obtained from said step b), 
 wherein: 
 said step b) controls the coding scheme according to the result of classification in said step c); and 
 said step d) controls a decoding scheme according to the result of classification in said step c). 
 
   
   
     11. The coding and decoding method as claimed in  claim 10 , wherein said step b) comprises the steps of a1) restricting a frequency band of the image data on the non-edge block, and a2) performing down-sampling on the image data having undergone said step a1). 
   
   
     12. The coding and decoding method as claimed in  claim 10 , wherein said step d) comprises the steps of d1) restricting a frequency band of the coded data on the non-edge block, and d2) obtaining pixel values through interpolation operation therefrom. 
   
   
     13. The coding and decoding method as claimed in  claim 11 , wherein said step a1) controls filter coefficients applied according to a set image characteristic mode. 
   
   
     14. The coding and decoding method as claimed in  claim 12 , wherein said step d1) controls filter coefficients applied according to a set image characteristic mode. 
   
   
     15. A coding method comprising the steps of:
 a) dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; and 
 b) coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks, 
 wherein said step b), for the edge block, obtains an average of maximum value and minimum value in pixel value on each block as a first code assignment threshold, subtracts a predetermined value from the first code assignment threshold so as to obtain the subtraction result as a second code assignment threshold, and performs coding by using the second code assignment threshold as a reference therefor. 
 
   
   
     16. The coding method as claimed in  claim 15 , further comprising the step of c) determining whether an image region is a character image region mainly including a character, wherein said step b) performs coding by using the second code assignment threshold when the input image region is the character image region, while otherwise using the first code assignment threshold. 
   
   
     17. The coding method as claimed in  claim 15 , further comprising the step of c) controlling the predetermined value according to a set image characteristic mode. 
   
   
     18. A coding and decoding device, comprising:
 a part classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and 
 a part decoding coded data according to a linear interpolation scheme for generating pixel values included in the non-edge part. 
 
   
   
     19. The device as claimed in  claim 18 , wherein, when a picture regarding mode is selected, the input image is coded according to a coding scheme prepared for the non-edge parts is applied regardless of result of classification of said classifying part. 
   
   
     20. A coding and decoding device, comprising:
 a part classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and 
 a part decoding coded data according to a cubic-function convolution interpolation scheme for generating pixel values included in the non-edge part. 
 
   
   
     21. The device as claimed in  claim 19 , wherein, when a picture regarding mode is selected, the input image is coded according to a coding scheme prepared for the non-edge parts is applied regardless of result of classification of the classifying part. 
   
   
     22. A coding and decoding device, comprising:
 a part classifying an input multi-level image into edge parts and non-edge parts according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge parts and non-edge parts; and 
 a part decoding coded data according to an interpolation scheme having smoothing performance for generating pixel values included in the non-edge part. 
 
   
   
     23. The device as claimed in  claim 22 , wherein, when a picture regarding mode is selected, the input image is coded according to a coding scheme prepared for the non-edge parts is applied regardless of result of classification of said classifying part. 
   
   
     24. A coding device comprising:
 a part dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; and 
 a part classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part, 
 wherein said coding part controls the coding scheme according to the result of classification of said classifying part. 
 
   
   
     25. A coding device comprising:
 a part dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; and 
 a part classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part, 
 wherein said dividing part controls a determination threshold therefor according to the result of classification of said classifying part. 
 
   
   
     26. A coding device comprising:
 a part dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; and 
 a part classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part, 
 wherein said dividing part controls a determination threshold thereof according to the result of classification of said classifying part and a set image characteristic mode. 
 
   
   
     27. A coding and decoding device comprising:
 a part dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; 
 a part coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks; 
 a part classifying the input multi-level image into a halftone-dot part mainly including halftone dots and the other non-halftone-dot part; and 
 a part decoding coded data obtained from said step b), 
 wherein: 
 said coding part controls the coding scheme according to the result of classification of said classifying part; and 
 said decoding part controls a decoding scheme according to the result of classification of said classifying part. 
 
   
   
     28. The coding and decoding device as claimed in  claim 27 , wherein said coding part comprises a part restricting a frequency band of the image data on the non-edge block, and a part performing down-sampling on the image data having been processed by said restricting part. 
   
   
     29. The coding and decoding device as claimed in  claim 27 , wherein said decoding part comprises a part restricting a frequency band of the coded data on the non-edge block, and a part obtaining pixel values through interpolation operation therefrom. 
   
   
     30. The coding and decoding device as claimed in  claim 28 , wherein said restricting part controls filter coefficients applied according to a set image characteristic mode. 
   
   
     31. The coding and decoding device as claimed in  claim 29 , wherein said restricting part controls filter coefficients applied according to a set image characteristic mode. 
   
   
     32. A coding device comprising:
 a part dividing an input multi-level image into a plurality of blocks, and determining whether each block is an edge block or a non-edge block according to edge degree thereof; and 
 a part coding the input multi-level image according to a coding scheme different between the edge blocks and non-edge blocks, 
 wherein said coding part, for the edge block, obtains an average of a maximum value and minimum value in pixel value on each block as a first code assignment threshold, subtracts a predetermined value from the first code assignment threshold so as to obtain the subtraction result as a second code assignment threshold, and performs coding by using the second code assignment threshold as a reference thereof. 
 
   
   
     33. The coding device as claimed in  claim 32 , further comprising a part determining whether an image region is a character image region mainly including a character, wherein said coding part performs coding by using the second code assignment threshold when the image region is the character image region, while otherwise using the first code assignment threshold. 
   
   
     34. The coding device as claimed in  claim 32 , further comprising a part controlling the predetermined value according to a set image characteristic mode.